This invention relates to syringes and has for its object an autodestruct syringe, that is, one that can be used once only and is rendered disabled by the user during the process of normal use.
Since the early 1980""s the spread of AIDS, Hepatitis and other diseases has partly occurred due to the reusing of syringes. The majority of syringes are of a disposable nature, being easy to manufacture in plastics and are often marked xe2x80x9cUse once and destroyxe2x80x9d. However there is no inbuilt barrier within the product to prevent it from being used more than once and by more than one person.
Drug abusers have certain ritualistic techniques that must be fully accommodated if an autodestruct syringe design is to be successful and accepted in this vital market segment. Drug abusers can require to insert a needle many times before a suitable injection site is found, and make numerous small insertions and withdrawals during this process. After an injection a user may choose to flush out any drug left in the xe2x80x9cdead spacexe2x80x9d of the syringe with their own blood several times.
The primary area of concern with the spread of the previously mentioned diseases is that of the drug abuser, but all areas can benefit from such a syringe, if it in no way hinders the user in the use of it.
Many attempts have been made to provide such an autodestruct syringe and examples of designs are shown in U.S. Pat. No. 3,951,196, U.S. Pat. No. 4,220,157, U.S. Pat. No. 4,252,118, GB-A-2184657, U.S. Pat. No. 3,478,937, U.S. Pat. No. 4,367,738, and EP-A-029017. However, to date no design has reached the market, either because of complexities in manufacture, or increase in costs. Furthermore earlier designs have not been suitable for the variety of techniques employed by users, in particular the drug abusers, and may not feel xe2x80x9cnormalxe2x80x9din use.
Some previous designs have used projection means within the barrel. These however may disrupt the forward motion of the plunger during the injection, and can be xe2x80x9cfeltxe2x80x9d by the user. This is caused by the interaction with the projection means by an elastomeric cap affixed to the plunger.
Other designs have a breakable means inbuilt to the design so that part of the plunger separates leaving the syringe inoperable. This can be a health risk as it leaves an unprotected piece of broken plastic which has recently been inside a barrel possibly containing contaminated blood. By the removal of part of the plunger the barrel is further exposed to abuse and possible conversion to a working unit. Some previous ideas have only been operable in a syringe with an integrated needle as this protects them from tampering and subsequent reuse.
Therefore the ideal product is one which fits closely in with the current manufacturing techniques and assembly procedures, offers no resistance to the user, and is truly autodestruct so that it cannot be tampered with.
According to the first aspect of the present invention, a syringe comprises a barrel having a plunger in slidable and sealing engagement therein, in which the barrel has at least one means interrupting a cylindrical surface of its inner wall, and the plunger has a locking means, the arrangement being such that the locking means operates on engagement with an interruption means on withdrawal of the plunger to prevent further withdrawal movement.
The arrangement allows for use of the syringe in a normal way but is rendered unfit for further use after one injection by operation of the locking means.
Preferably, an interruption means is arranged adjacent the distal end of the barrel. The distal end is the end to which the needle is attached. It is not possible to withdraw the plunger further than the distal end interruption means once the injection has taken place. The interruption means may be positioned to allow flushing after a full injection, but prevent refilling of the barrel. A further interruption means may be located at the proximal end of the barrel. This prevents removal of the plunger prior to use, which would serve as a total tamper proof feature.
The interruption means is preferably arranged at an angle other than 90xc2x0 to the longitudinal axis of the barrel. This allows friction between the plunger and the interruption means to be dissipated as only part of the interruption means is in contact with the plunger at any one moment. The interruption means preferably extends round the whole circumference of the barrel.
Each interruption means may be a projection. Quite a small projection enables the locking means to operate, and if arranged at an angle will not disrupt the forward motion of the plunger, so that it is not xe2x80x9cfeltxe2x80x9d by the user.
Preferably however each interruption means comprises a groove. Grooves offer no resistance to the plunger, so that a normal feel to the injection is achieved. They are also more positive in ensuring operation of the locking means.
It would also be possible for the interruption means to comprise a groove followed by a projection.
Angled grooves and projections are much easier to produce by injection moulding than those at right angles to the barrel axis.
Each projection or groove is preferably of substantially triangular cross-section, with a first edge inclined slightly to the cylindrical surface, and a second edge inclined sharply to the cylindrical surface. The first edge allows normal forward movement of the plunger, while the second edge engages the locking means on withdrawal movement. The first edge is preferably at an angle of between 20xc2x0 and 30xc2x0 to the cylindrical surface. The second edge is substantially perpendicular to the first edge, and at an angle of between 60xc2x0 and 70xc2x0 to the cylindrical surface.
Preferably the head of the plunger has means, such as a peg, with which an elastomeric sealing cap engages, and the locking means is also arranged on the head of the plunger, adjacent the cap. The plunger head locks into the interruption means and jams, effectively rendering the syringe useless. The plunder remains intact, filling the barrel, and acting as an anti-tamper block. If excess effort is applied in the removal it may break at the joint between the stem of the plunger rod and head. However, this is not the object of the design as the locking feature is more than adequate to prevent reuse and the more preferable.
The locking means preferably comprises two rearward facing flukes attached to the head by a flexible connection, movable in each direction but engaging with the interruption means on withdrawal movement away from the distal end of the barrel. When engaging with for example an angled groove the head of the plunger is deflected in the barrel perpendicular to the groove so that both flukes are located in the groove, as far as the flexibility of the connection and the elasticity of the elastomeric cap will permit. Alternatively, the locking means comprises a disc attached to the head, and having a flexible periphery which slides in either direction, but engages with the interruption means on withdrawal movement. It is preferably held by the head in the locked position. The disc may be cross-shaped.
The design can be incorporated into a syringe product with or without an integrated needle. However the present invention benefits from being tamper proof in an open luer type syringe barrel and in a barrel with an integrated needle.
The invention also has the advantage that the syringe is made of two plastics parts manufactured by injection moulding, being the barrel and the plunger. The plunger is made with the peg over which the elastomeric cap is fitted to engage and seal with the inner wall of the barrel.
The plunger is moulded in a traditional mould which can be manufactured to include either of the modifications described. Alternatively a new or existing mould can be fitted with inserts which relate to this fluke/connection or disc area. This means an existing product can be changed to include the modification of this invention for relatively low capital costs. Likewise the barrel described in this invention can be produced through modification of the moulding cores for the barrel, which again is only a fraction of the total capital for such a moulding tool.
Further aspects of the invention relate to apparatus for making a syringe plunger including the locking means.
According to a second aspect of the invention, apparatus for making a syringe plunger adapted to slide in a syringe barrel and having a locking means adapted to engage an interruption means in the inner wall of the barrel comprises a two-part moulding tool, each part bearing an impression of a portion of the plunger such that the two parts co-operate to make the whole plunger, and each part having a removable insert bearing the impression for the locking means for the respective plunger portion.
According to a third aspect of the invention, an insert is adapted to be used in apparatus for making a syringe plunger adapted to slide in a syringe barrel and having a locking means adapted to engage an interruption means in the inner wall of the barrel the apparatus comprising a two-part moulding tool, each part bearing an impression of a portion of the plunger such that the two parts co-operate to make the whole plunger, the insert bearing the impression for the locking means of the respective plunger portion and being adapted to be mounted removably in the corresponding tool part.
The second and third aspects of the invention enable moulding tools for existing plungers to be modified to include the inserts with the locking means. The existing plungers can therefore be readily changed to include the locking means, but with low capital costs, as complete new tools are not required.
Further the inserts can themselves be readily changed. The moulding tool wears with use, but wear to the portion containing the locking means is critical, as it can render the locking means inoperable. The amount of acceptable wear for the locking means is much less than that for the rest of the plunger. The inserts with the locking means can therefore be changed often, to ensure accurate manufacture of the locking means.
The inserts may be located at an existing split line in a tool part. Each insert may be attached to the tool part by pins inserted in aligned openings in the insert and tool part. Alternatively they may be secured by packing.
It is also possible for the tool part to be provided with cavities for receiving the insets. The cavities may be cut or machined in the tool part.
Each insert may comprise one or more plates.